Wood panel constructiony



1811. 1956 D. c. CRAWFORD woon PANEL CONSTRUCTION Filed July 17, 1951 5 i M5 1 Mf W Li? WM L, 3: 9 0 T H j 9% M vi 5 kW i f 1 g Wt/M M 1 g 7 2 z 9 n l swwum Z 1 i 7, w

WOOD PANEL CONSTRUCTION David C. Crawford, Grosse Pointe Woods, Mich.

Application July 17, 1951, Serial No. 237,208

6 Claims. (Cl. 20-91) This invention relates to wood panel constructions, and especially to a type of construction suitable for wood panels having flush faces such as are used in garage doors and other assemblies.

In the past, wood panels have been constructed having flush faces for use in such constructions as garage doors of the type having a plurality of elongated panels hinged together which may be rolled upwardly above the door frame. The main problem in flush door construction has been that of preventing bowing, that is, the tendency of the panels to bend transversely under moisture conditions due to the higher expansion rate of the face material compared with the wood frame. Until now, to avoid this bowing it has been necessary to counteract the overexpansion of the face member by providing an equal amount of face material on the opposite side of the door frame, the bending moments of the two face materials balancing each other to prevent bowing. This construction has several important disadvantages, since the cost is greatly increased due to the larger amount of material and the additional labor required. Moreover, in the case of garage doors, the back panel member is extraneous in that it serves no purpose in enhancing the appearance of the door, being ordinarily not visible.

It is an object of this invention to overcome these disadvantages and to provide an improved wood panel construction of the flush type using a minimum amount of material, but wherein the bowing tendency is substantially prevented by a novel arrangement and construction.

It is another object to provide a wood panel construction of the above charactenusing only one face memher for the outside of the door and utilizing the principle of a planned or predetermined balance of expansive forces with unequal amounts of material. More particularly, it is an object to provide a panel construction wherein a small amount of high-expansion rate material is applied to the back side of the frame to counteract the relatively large amount of face material on the front of the frame, this counteraction being accomplished by novel and improved methods for constructing the frame or for attaching the materials to the frame which result in a greater bowing tendency, per unit of area, in the backing material than in the face material.

It is also an object, in one form of my invention, to provide an improved door panel construction of the above character, in which narrow strips of face material are secured along the back of the frame members, and in which a plurality of transverse slots are cut in the frame members to shift the neutral bending axis of these members, whereby the leverage of the narrow backing strips is multiplied so as to counteract the bowing tendency of the face member.

It is another object, in another form of my invention, to provide an improved panel construction having back ing strips of face material along the frame members, these backing strips being secured to the frame members in a more resistant manner than the front face member. More particularly, it is an object to provide a panel in I v United States Patent O F 2,732,598 Patented Jan. 31, 1956 which the face material is secured to the frame by nails or similar pin fasteners whereas the backing strips are secured to the frame by gluing or a like bond, whereby the expansion of the backing strips will have more effect on the frame than the bowing tendency of the face member.

It is a further object, in another form of my invention, to provide a wood panel construction having a flush face member and thin backing strips as described, the backing strips being of a higher expansion rate than the face material, whereby the moment forces of these backing strips will counteract the bowing tendency of the face member.

Other objects, features, and advantages of the present invention will become apparent from the subsequent description taken in conjunction with the accompanying drawings.

In the drawings:

Figure l is a perspective view, with parts broken away for clarity, showing an improved wood panel according to one form of my invention, with transverse slots in the longitudinal frame members;

Fig. 2 is a cross-sectional view taken along the line 22 of Fig. 1 and showing the relation of the backing strips to the frame members;

Fig. 3 is a cross-sectional view taken along the line 33 of Fig. 1 and showing the arrangement of the slots; and

Fig. 4 is a cross sectional view similar to Fig. 2 but showing a modified construction using nails for the face member and glue for the backing strips.

The novel panel construction comprises in general a rectangular frame, a face member secured to one side of the frame so as to present a fiush surface, and a pair of backing strips secured to the back of the longitudinal frame members. These backing strips have a greater bowing tendency, per unit of area, than the face member and are thus used to counteract the bowing tendency of the face member. In one form of the invention this is accomplished by providing a plurality of transverse slots along the back of the longitudinal frame members, these slots extending partially into the frame members so as to shift their neutral bending axes toward the face member. This results in imparting to the backing strips a greater leverage whereby the bending moments on both sides of the frame are equalized. in another form of the invention, the backing strips are secured by glue or a similar bond to the frame members, whereas the face member is secured thereto by nails or similar pin fasteners. In this manner, the expansion of the backing strips has a greater effect thanthat of the face member, since the nails tend to yield under bending stress more than the glued bond. In a third modification, the bowing tendency of the backing strips is increased by the use of material having a higher moisture expansion rate than that of the face member. It will be understood that these forms of the invention are not mutually exclusive, but rather that any combination of these methods of construction could be provided in a panel.

Referring more particularly to the drawings, Figs. 1 to 3 show a panel generally indicated at 11, this panel being of a type such as is used in constructing multisection garage doors which may be rolled on tracks above the door frame. The panel comprises a rectangular frame, generally indicated at 12, a flush face member 13 secured to one side of the frame, and backing strips 14, 15, 16, and 17 secured to the back surface of the frame.

As is best seen in Fig. l, the frame comprises upper and lower longitudinal frame members 18 and 19, respeetively, these members being connected by one or more intermediate frame members 20 and by side frame members 21 and 22. These frame members are constructed of conventional lumber such as pine or fir having a relatively low moisture expansion retain a longitudinal direction The face member 13 is of a relatively high expansion material, suchas plywood, and extends to the outermost dimensions of the frame so as to present a flush and uninterrupted surface. It is apparent that if the frame 11 and the face-member 13 are considered in combination, the tendency of the face member to expand at a higher rate than the frame will cause bowing of the longitudinal frame members 18 and 19. This bowing would normally be such as to cause the opposite ends of the panel to rise from the plane of the paper, as seen in Fig. 1.

The means for counteracting this bowing tendency comprises mainly the backing strips 14 and 15, which in the embodiment of Figs. 1 to 3 are constructed of highexpansion material similar to that of face member 13. These backing strips are preferably of the same width as the longitudinal frame members 18 and 19 and are secured along the back of these frame members. It will be seen that if the backing strips 14 and 15 and the frame 11 are considered alone, the higher expansion rate of the backing strips will cause bowing of the frame in a direction opposite to that caused by face member 13. However, since the area of the backing strips is substantially less than that of face member 13, this bowing tendency will be much weaker than that of the face member.

To increase the effectiveness of the bowing tendency of backing strips 14 and 15, a plurality of slots 23, such as saw cuts, are provided along the back surfaces of frame members 18 and 19. The number and spacing of these slots is not critical, although in the conventional door section they could be spaced roughly four inches apart. The depth of these slots may be approximately half the thickness of the frame members, and it will be noted that these slots are in a direction across the grain of the frame members. These slots serve the purpose of shifting the neutral bending axis of the longitudinal frame members 18 and 19 toward the face panel 13.

As a result of this construction, moisture tending to expand the panel members will cause the backing strips 14 and 15 to have a greater effect than would normally be the case, since the leverage is increased due to the shifting of the neutral axis. The arrangement is such that this increased leverage substantially balances the bowing tendency of the face member so that the panel assembly will show substantially no bowing along its length.

It will be observed that aside from the result just described, this construction has several other important advantages. For one thing, low-grade lumber can be used for the frame members, since the backing strips completely cover the frame. The backing strips 16 and 17 serve to cover the back of frame members 21 and 22 and may be used to conceal the joints 24 of the frame members. Another advantage of the improved construction is that short pieces of lumber may be used for the frame members, since their joints are covered by the backing strips. Furthermore, the construction only requires the conventional fabricating machinery and thus minimizes the cost of manufacture.

Fig. 4 illustrates a modification of-the invention, generally similar in principle to that of Figs. 1 to 3, but in which the prevention of bowing is accomplished by a novel method of securing the face member 25 and backing strips 26 and 27 to the frame members 28 and 29. In this embodiment, the face member 25 is secured to the frame members by nails or similar pin fastener 31, whereas the backing strips are secured to the frame members by a bond, such as glue, shown at 32. It is known that a face material glued to a frame will how it more than a similar face material nailed to the frame, for the reason that during expansion the nails give slightly to relieve the strain. For this reason, the backing strips, even though of smaller total area than the face member will effectively counteract the bowing tendency of the face member and maintain the panel in unbowed condition. As a third type of construction, not readily shown by illustration, the backing strips may be of material hav- 7 ing a higher expansion rate than that of the face member. In this manner, equal moisture conditions on both sides of the panel will cause greater linear expansion of the backing strips than of the face panel, and the increased bending moment on the back of the panel will counteract the bowing tendency of the face member.

While each of these types of construction have been described separately, it is apparent that any combination of these constructions is possible in a particular panel assembly. For example, the construction shown in Fig. 4 may be further modified by providing slots similar to slots 23 in frame members 28 and 29, thus adding to the leverage of strips 26 and 27. Furthermore, the latter strips could be fabricated of material having a higher expansion rate than that of face member 25. It will also be understood that while the invention is only shown as applied to a rectangular panel having a tendency to bow primarily in one direction, the principles of the invention could as well be applied to panels of such shape as to tend to bow in two directions. For example, in the embodiment of Figs. 1 to 3, the side frame members 2.1 and 22 could be provided with a plurality of slots similar to slots 23, the backing strips 16 and '17 thus serving to counteract the bowing tendency of the panel in a vertical plane.

While it will be apparent that the preferred embodiments of the invention herein disclosed are well calculated to fulfill the objects above stated, it will be appreciated "that the invention is susceptible to modification, variation and change without departing from the proper scope or fair meaning of the subjoined claims.

What is claimed is:

l. A wood panel assembly comprising a frame having oppositely disposed frame members, a face member secured to only one side of said frame members, said face member being fabricated of material having a higher rate of expansion than that of the frame members, a pair of spaced backing strips secured to the other side of said frame members, said backing strips also being fabricated of material having a higher expansion rate than said frame members and having a total area less than that of said face member, and means causing said backing strips to eoact with said frame members to counteract the tendency of said face member to bow said frame members.

2. In a wood panel construction, a frame having oppositely disposed longitudinal frame members, a face member secured to only one side of said frame members, said face member being fabricated of material having a higher rate of expansion in a longitudinal direction than said frame members, a pair of spaced backing strips secured to the other side of said frame members, the total area of said backing strips being less than that of said face member, said backing strips also being fabricated of material having a higher rate of expansion than said frame members, and means for causing the bowing force of said backing strips, per unt of area, on said frame members in one direction to be greater than the bowing force, per unit of area, of said face member on said frame members in the opposite direction.

3. In the construction of a wood panel, a frame having oppositely disposed longitudinal frame members, a face member secured to one side of said frame, said face member being fabricated of material having a higher rate of expansion than said longitudinal frame members whereby said face member will tend to bow said frame members in one direction, a pair of backing strips secured to the other side of said frame members, said backing strips also being fabricated of material having a higher expansion rate than said frame members and tending to bow said frame members'in a direction opposite to the bowing tendency of said face member, the total area of said backing strips being substantially less than that of said face inetnber, and means for multiplying the bowing tendency of said backing strips whereby the backing strips counteract the bowing tendency of said face member.

4. A wood panel construction comprising a frame having oppositely disposed longitudinal frame members, a face member secured to the front side of said frame, said face member having a higher rate of expansion than said frame members and tending to bow said frame members in one direction, a pair of backing strips secured to the back surfaces of said frame members, the total area of said backing strips being substantially less than that of said face member, said backing strips likewise being of higher expansion material than said frame members and tending to bow said frame members in the opposite direction, and a plurality of transverse slots on the back surfaces of said frame members, said slots extending partially into said frame members, whereby the neutral bending axes of the frame members is shifted toward said face member.

5. A wood panel assembly construction comprising a frame having oppositely disposed longitudinal frame members, a face member secured to only one side of said frame, said face member being fabricated of material having a higher expansion rate than said frame members, and a pair of backing strips secured to the other side of said frame members, said backing strips being fabricated 6 of material having a higher expansion rate than said face member, whereby the bowing tendency of said backing strips, per unit of area, is greater than that of said face member.

6. A wood panel construction comprising a frame having oppositely disposed longitudinal frame members, a face member having a higher rate of expansion than said frame member, pin type fasteners securing said face member to one side of said frame whereby said face member tends to bow said frame members in one direction, a pair of backing strips having a higher expansion rate than said frame members and a total area less than that of said face member, and an adhesive bond securing said backing strips along the other side of said longitudinal frame members, whereby said backing strips tend to bow said frame members in the opposite direction.

References Cited in the file of this patent UNITED STATES PATENTS 1,777,317 Land Oct. 7, 1930 2,153,715 Kahr Apr. 11, 1939 2,199,938 Kloote May 7, 1940 2,354,725 Weyerhaeuser Aug. 1, 1944 FOREIGN PATENTS 194,336 Great Britain Mar. 8, 1923 

